Part I: Frequency Offset Acquisition and Tracking Algorithms

Wireless receivers process signals that bear information as well as disturbances caused by the transmitter/receiver circuits and channel impairments such as fad:ing, interference, and additive white gaussian noise (AWGN). Usually, the receiver knows only some statistical properties of the signal and disturbances. From these statistical properties and using a finite observation of the received signal, the receiver is able to estimate the transmitted data symbols. The receiver makes the decision on the received data using locally generated symbol clock and carrier oscillator, both of which are not referenced to the actual versions used to generate the data at the transmitter. The receiver has to estimate the offset between locally generated carrier and symbol clock to those used at the transmitter. Clock mismatches are labeled as time jitters, while local carrier mismatches are labeled either as phase rotation errors or frequency offset errors. Carrier phase recovery is the process known as carrier tracking, where the receiver estimates the offset between the local oscillator phase and the actual phase of the transmitted carrier. Carrier frequency offset recovery is known as carrier acquisition, and it is the process of estimating the offset between the frequency drift/change of the local oscillator and the actual (received) carrier frequency transmitted at the transmitter. The methods in which the receiver estimates carrier mismatches can be feed forward (open Loops) or feedback (closed loops) synchronization. Feed forward method is characterized by the absence of hang up and cycles slips, and fast and accurate acquisition. Such advantages are absent with conventional feedback synchronizers such as Costas loop. Another advantage of feed forward algorithms is that the synchronizer can be fully implemented using digital signal processing techniques as shown in figure 1.